Method and apparatus for registering 3D models of anatomical regions of a heart and a tracking system with projection images of an interventional fluoroscopic system

ABSTRACT

An imaging system for use in a medical intervention procedure is disclosed. A first image acquisition system is configured to produce a fluoroscopy image of an anatomical region. A second image acquisition system is configured to produce a 3D model of the anatomical region. An interventional tracking system, which includes a position indicator, is configured to maneuver within the anatomical region. A first anatomical reference system is common to both the first and the second image acquisition systems, and a second anatomical reference system is common to both the first image acquisition system and the interventional tracking system. A processing circuit configured to process executable instructions for registering the second image acquisition system with the first image acquisition system to define a first registration, registering the interventional tracking system with the first image acquisition system to define a second registration, and in response to the first and second registrations, registering the interventional tracking system with the second image acquisition system.

BACKGROUND

This invention relates generally to a medical imaging system, and moreparticularly to a method and apparatus for registering 3D models ofanatomical regions with an interventional tracking system throughprojection images of the same anatomical regions obtained with afluoroscopy system.

During a number of interventional procedures related to the improvementof electrical therapy in the heart, the physician has to manipulatecatheters and/or leads inside the heart chambers. An example of the twomost complex and common procedures include atrial fibrillation (AF)ablation, and bi-ventricular pacing.

Atrial fibrillation, an arrhythmia in which the atria (upper chambers ofthe heart) stop contracting as they fibrillate, is the most common ofthe heart rhythm problems. In United States alone it is estimated thatthere are over 2 million people who have atrial fibrillation. Presentdata suggest that it is the most common arrhythmia-related cause ofhospital admissions. Patients with AF tend to have a high incidence ofsuch complications as stroke and congestive heart failure. Prematureatrial contractions may act as triggers and initiate paroxysms of AF.These premature atrial contractions have been shown to predominantlyoriginate in the pulmonary veins from the left atrium. Since infrequentand non reproducible premature atrial contractions may limit the utilityof ablating trigger sites, a variety of surgical and catheter techniqueshave been used to isolate the pulmonary veins from the left atrium.

One of the surgical techniques used to treat (ablate) AF involvesapplications of radiofrequency waves to create small scars on theheart's surface near the connection between the pulmonary veins and theleft atrium. The small scars created by the radiofrequency waves tend tostop the erratic impulses of AF by directing the impulses to follow anormal electrical pathway through the heart. Typically, this type ofsurgical procedure is performed through a chest incision. Surgeons usespecially designed instruments to deliver radiofrequency waves to theabnormal tissue, typically during the open heart surgery performed forother reasons, such as valve surgery or bypass surgery for example.Although this type of surgical technique is effective when the patientis undergoing open heart surgery for another reason, catheter-relatedtreatment methods are more practical when the patient does not requirethe invasive open heart surgery for other reasons.

One of the catheter techniques involves fluoroscopic guided positioningof catheter in the left atrium after going through a blood vessel, andthe application of radiofrequency energy at areas showing doublepotentials suggestive of sites capable of conducting between the leftatrium and the pulmonary veins. It has also been shown that ablation atother sites such as between the mitral valve and left pulmonary veins,and between the pulmonary veins, as is done during the surgicalintervention, may increase the success rate of AF ablation. Thethree-dimensional reconstruction of the left atrium using some currentlyavailable technologies, the inability of the physician to visualize thepulmonary vein ostia (opening of these veins into the left atrium) frominside, the varying size of the pulmonary veins and thus the pulmonaryvein ostia, the difficulty in keeping the mapping and ablation cathetersstable at the pulmonary vein ostial site due to the complex 3D geometryof these areas, all make current approaches to mapping and ablationusing current fluoroscopically guided techniques somewhat cumbersome andlengthy. Because of these limitations, surgery has been preferred overradiofrequency catheter ablation, especially in patients with persistentatrial fibrillation, and it is estimated that less than 20 percent ofpatients with persistent AF undergoing radiofrequency ablation for AF,benefit from this approach.

A factor that may be associated with the above mentioned limitation isthat the operator typically guides an interventional tool using mainlythe fluoroscopy images. A typical task in such a procedure is theplacement of a catheter at a specific location, such as one of thepulmonary veins for example. These anatomical structures are not welldepicted by the x-ray system since they do not present contrast versusthe surrounding anatomical structures.

The medical task would be much easier if these target anatomicalstructures were visible in the fluoroscopy image in the precise anatomicfashion separate from the surrounding anatomic structures.

Another important procedure, as mentioned above, involves bi-ventricularpacing in the treatment of heart failure. Despite considerable progressin the management of congestive heart failure (CHF), it remains a majorhealth problem worldwide. It is estimated that there are 6-7 millionpeople with CHF in the United States and Europe, and approximately 1million patients are diagnosed with CHF every year.

Despite significant advances in the treatment of CHF using variouspharmacological therapies, quality-of-life in patients with CHF is pooras they are frequently hospitalized, and heart failure is a common causeof death. In addition, there is significant cost attached to thisproblem.

Normal electrical activation in the heart involves activation of theupper chambers, called the atria, followed by simultaneous activation ofboth the right and the left lower chambers, called the ventricles, bythe left and right bundle branches. As patients with advanced CHF mayhave conduction system disease, which may play a role in worseningcardiac function, pacing therapies have been introduced in an attempt toimprove cardiac function. One frequently noted conduction abnormality isleft bundle branch block (LBBB). In one study, (Xiao H B, et al.Differing effects of right ventricular pacing and LBBB on leftventricular function. Br Heart J 1993; 69:166-73) 29% of patients withCHF had LBBB. Left bundle branch block delays left ventricular ejectiondue to delayed left ventricular activation as the electrical impulse hasto travel from the right to the left side leading to sequential ratherthan simultaneous activation, as mentioned before. In addition,different regions of the left ventricle (LV) may not contract in acoordinated fashion.

Cardiac resynchronization, also knows as Bi-Ventricular (Bi-V) pacing,has shown beneficial results in patients with CHF and LBBB. During Bi-Vpacing, both the right and the left ventricle (RV, LV) of the heart arepaced simultaneously to improve heart pumping efficiency. It has alsobeen shown recently that even some patients with no conduction systemabnormalities, such as LBBB, may also benefit from the Bi-V pacing.During Bi-V pacing, in addition to the standard right atrial and rightventricular lead used in currently available defibrillators orpacemakers, an additional lead is positioned into the coronary sinus.The additional lead is then advanced into one of the branches of thecoronary sinus overlying the epicardial (outer) left ventricularsurface. Once all of the leads are in place, the right and leftventricular leads are paced simultaneously, thus achievingsynchronization with atrial contraction.

There are, however, several problems with this approach. First, thistype of procedure is time-consuming. Second, placement of the LV lead islimited to sites available that provide reasonable pacing and sensingparameters. And third, cannulating the coronary sinus may be challengingas a result of an enlarged right atrium, rotation of the heart, orpresence of Tebesian valve (a valve close to the opening of the coronarysinus). Coronary sinus stenosis (occlusion) has also been reported inpatients with prior coronary artery bypass surgery, further complicatingthe problem.

In most instances, problems with the placement of the coronary sinuslead are identified at the time of the interventional procedure. In theevent of the coronary sinus lead placement procedure being abandoned,the patient is brought back to the operating room and the LV lead ispositioned epicardially. During this procedure, an incision is made onthe lateral chest wall and the lead is placed on the outer side of theleft ventricle.

Unfortunately, there are many problems with epicardial lead placement aswell, some of which include but are not limited to:

Limited view of the posterolateral area of the left ventricle using theincision of the chest wall, also called minithoracotomy;

The limited number of placement sites providing reasonable pacing andsensing parameters;

Inability to identify the most appropriate location and placement of thelead at the most appropriate site;

Potential risk of damaging the coronary arteries and venous system; and

Difficulty in identifying the ideal pacing site as a result of one ormore of the above limitations.

It has also been shown that LV pacing alone may be as effective as Bi-Vpacing. However, due to the unstable nature of the coronary sinus lead,a pacing and sensing lead is usually placed in the right ventricle incurrently used techniques.

Cardiac CT may be used to create a roadmap of coronary sinus and leftventricular anatomy such that appropriate sites may be identified forthe placement of a LV pacing lead for Bi-V/LV pacing, either at the mostappropriate branch of the coronary sinus, or on the left ventricularwall epicardially (from outside). CT or MR imaging may also identifyareas devoid of blood vessels and nerves, as well as scar tissue. Thesemodalities may also be used to determine the asymmetric contraction ofthe ventricles and identify different regions of the ventricles notcontracting in a coordinated fashion. The presence of scarring fromprevious heart attacks may make this uncoordinated contraction evenworse.

During an interventional procedure, the operator may guide aninterventional tool using mainly the fluoroscopic images. However,strategically important anatomical structures, such as the left atriumand pulmonary veins in the case of AF interventional procedure planningand the coronary sinus and its branches in the case of bi ventricularpacing planning, for example, are not depicted by the x-ray system sincethey do not present contrast versus the surrounding anatomical makeup.Accordingly, the medical interventional task would be much easier ifthese target anatomical structure were visible in the fluoroscopicimage.

In some cases, the operator may also use an interventional trackingsystem having a catheter-based tracking system equipped withnavigational functionality, which is able to provide the location of thecatheter in a given referential. However, navigational informationprovided by the probe is not displayed in the true 3D model.

While existing medical procedures may be suitable and appropriate forcertain medical conditions, significant procedural limitations stillexist. Accordingly, there remains a need in the art for an improvedmethod and apparatus for registering 3D models of anatomical regionswith projection images of the same, and for registering the 3D modelswith an interventional tracking system, to overcome these drawbacks.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention include an imaging system for use in amedical intervention procedure. A first image acquisition system isconfigured to produce a fluoroscopy image of an anatomical region. Asecond image acquisition system is configured to produce a 3D model ofthe anatomical region. An interventional tracking system, which includesa position indicator, is configured to maneuver within the anatomicalregion. A first anatomical reference system is common to both the firstand the second image acquisition systems, and a second anatomicalreference system is common to both the first image acquisition systemand the interventional tracking system. A processing circuit configuredto process executable instructions for registering the second imageacquisition system with the first image acquisition system to define afirst registration, registering the interventional tracking system withthe first image acquisition system to define a second registration, andin response to the first and second registrations, registering theinterventional tracking system with the second image acquisition system.

Other embodiments of the invention include a method of registering a 3Dmodel of an anatomical region of a patient with a catheter-basedtracking system, the catheter-based tracking system comprising acatheter with a position indicator. The catheter with the positionindicator is disposed within the anatomical region, and a fluoroscopyimage of the anatomical region is generated. A 3D model of theanatomical region is also generated. Using a first common anatomicalreference system and a discernible parameter associated with thecatheter, the 3D model is registered with the fluoroscopy image, therebydefining a first registration. Using a second common anatomicalreference system and signals from the position indicator representativeof the location of the catheter in the fluoroscopy image, thecatheter-based tracking system is registered with the fluoroscopy image,thereby defining a second registration. Using the first registration andthe second registration, the 3D model is registered with thecatheter-based tracking system.

Further embodiments of the invention include a computer program productfor registering a 3D model of an anatomical region of a patient with acatheter-based tracking system, the catheter-based tracking systemcomprising a catheter with a position indicator. The product includes astorage medium, readable by a processing circuit, storing instructionsfor execution by the processing circuit for carrying out some or allportions of the aforementioned method.

Yet further embodiments of the invention include a computer programproduct for registering a 3D model of an anatomical region of a patientwith projection images of the same from an interventional fluoroscopysystem. The product includes a storage medium, readable by a processingcircuit, storing instructions for execution by the processing circuitfor carrying out some or all portions of the aforementioned method, andfor monitoring the introduction of a catheter delivery apparatus intothe anatomical region of interest, navigating the catheter deliveryapparatus over the registered model to an anatomical site of interest,and using the catheter delivery apparatus to deliver therapy.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments, andwherein like elements are numbered alike:

FIG. 1 depicts a generalized schematic of an imaging system for use in amedical intervention procedure;

FIG. 2 depicts an expanded view of a portion of the system of FIG. 1;

FIG. 3 depicts a generalized flowchart of a process for implementing anembodiment of the invention using the imaging system of FIG. 1;

FIGS. 4A, B and C, depict an exemplary registration of a 3D model with afluoroscopy image in accordance with an embodiment of the invention;

FIGS. 5A, B, C, D, E and F, depict validation of the registrationprocess performed in accordance with an embodiment of the invention;

FIG. 6 depicts a generalized flowchart of a registration process inaccordance with an embodiment of the invention;

FIG. 7 depicts an exemplary catheter for use in accordance with anembodiment of the invention; and

FIG. 8 depicts an illustration of a probability region for use inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION

By using the 3D imaging capabilities of the CT and registering theseimages with projection images of the fluoroscopy system, pulmonary veinsand other areas involved with initiating and sustaining AF may be moreprecisely and easily identified, thereby improving the success rate froma catheter procedure.

Embodiments of the invention disclosed herein also provide a system andmethod by which 3D models of anatomical structures, such as the coronarysinus and left ventricle for example, may be registered with projectionimages of the fluoroscopy system, thereby allowing the pacing leads tobe navigated and placed at the most appropriate site,

By registering the tracking system in the referential of theinterventional fluoroscopy system, the success rate of AF ablation usinga catheter technique should be improved, and navigating the LV lead tothe most appropriate site should assist in improving the effectivenessof Bi-V or LV pacing.

Embodiments of the invention use the referential of the projectionimages of the interventional fluoroscopy system to register the trackingsystem in the referential of the interventional system. This isaccomplished after the 3D model of the anatomical region of interest hasbeen registered with the interventional fluoroscopy system. Registrationof the 3D anatomical region of interest obtained from an imaging andevice, such as a CT scanner, is performed with the fluoroscopy systemusing a tool, such as a catheter or a lead for example, placed in anarea of the anatomical region, such as the coronary sinus-or the rightventricle for example, by a physician. A detailed description ofembodiments of the invention is presented herein by way ofexemplification and not limitation with reference to the severalfigures.

FIG. 1 depicts a generalized schematic of an imaging system 100 for usein a medical intervention procedure, such as, for example, an AFablation procedure or a bi-ventricular procedure, for example. In anembodiment, the imaging system 100 includes: an imaging apparatus 110for generating cardiac image data, such as, for example, image data ofthe left atrium and the coronary sinus, a data acquisition system 120for acquiring the cardiac image data from imaging apparatus 110, anacquisition database 130 for storing the cardiac image data from dataacquisition system 120, an image generation system 140 for generating aviewable image from the cardiac image data stored in acquisitiondatabase 130, an image database 150 for storing the viewable image fromimage generation system 140, an operator interface system 160 formanaging the imaging apparatus 110 and the cardiac image data andviewable image in databases 130, 150, which may be combined into onedatabase, and a processing system 180 for analyzing and displaying theviewable image in database 150 and being responsive to operatorinterface system 160. Processing software in processing system 180includes instructions, and is therefore adapted, to analyze data anddisplay images, thereby converting processing system 180 from a generalprocessor into a specialized processor. Scanned data that is capable ofbeing converted into a viewable image is referred to herein as imagedata.

System communication links 210, 212, 216, 218 and database communicationlinks 220, 222 provide a means for signal communication amongst andbetween systems 110, 120, 140, 160, 180 and databases 130, 150.Communication links 210-222 may be hardwired or wireless. Operatorinterface system 160 may be a standalone input/output terminal or acomputer including instructions in a variety of computer languages foruse on a variety of computer platforms, such as but not limited to, forexample, DOS™-based computer systems, Apple™-based computer systems,Windows™-based computer systems, HTML-based computer systems,specialized program language-based computer systems, or the like.

Operator interface system 160 includes a processor 170, such as, forexample, a microprocessor (MP) or any other processing circuit suitablefor the purposes disclosed herein, for managing the imaging apparatus110, for managing the data acquisition and image generation systems 120,140, for processing and managing the information in acquisition andimage databases 130, 150, and for managing the processing at processingsystem 180. Operator interface system 160 also includes: a memory 200that contains specific instructions relating to medical scanningprocedures, user input means, such as, for example, a keyboard 162, anduser output means, such as, for example, displays 164, 166. In anembodiment, interface system 160 and processing system 180 may beintegrally arranged. Display 164 may be adapted for exam prescription,and display 166 may be adapted for visualization. Alternatively,displays 164 and 166 may be integrated into one display. Examprescription includes such input parameters as: CT scan or region ofscan control, fluoroscopy system control, data acquisition control, andthe like. Operator interface system 160 may also be employed during anactual interventional procedure to display both fluoroscopy images and3D CT images, as discussed below. During an actual medicalinterventional procedure, data port 205 accepts information from amedical probe, such as, for example, a catheter 260, thereby permittingdata analysis in a real-time fashion during the actual interventionalprocedure.

Imaging apparatus 110 includes an electrocardiogram (EKG) monitor 112that outputs R-peak events 114, which generally delineate the beginningof a heart cycle, through an interface board 116 into a scanner 118,such as a CT scanner for example, a fluoroscopy system 115, and apatient table 117. Scanner 118 and fluoroscopy system 115 arealternatively herein referred to as image acquisition systems. Theinterface board 116 enables synchronization between the scanner data andthe EKG monitor data. Alternatively, the interface board 116 may be usedto couple the EKG monitor 112 to the scanner 118. An example of aninterface board 116 is a Gantry interface board. An exemplary scanner118 is a cardiac computed tomography (CT) system with support forcardiac imaging, ECG gated reconstruction followed by segmentationreconstruction of 3D models (in diastolic phase) allows imaging of theheart free of motion. During sinus rhythm, segmentation reconstructionwill be done at 75% of cardiac cycle (in diastole). Phase location isselected at around 45% of the cardiac cycle where the patient is inatria fibrillation. This phase is chosen as the R-R intervals areshorter. However, the illustrated scanner 118 is for exemplary purposesonly; other imaging systems known in the art may also be used. Examplesof other imaging systems include, but are not limited to, X-ray systems(including both conventional and digital or digitized imaging systems),magnetic resonance (MR) systems, positron emission tomography (PET)systems, ultrasound systems, nuclear medicine systems, and 3Dfluoroscopy systems. Imaging apparatus 110 may have both a scanner 118and a fluoroscopy system 115 for use as disclosed here, or imagingsystem 100 may have two imaging apparatuses 110, 110′, with imagingapparatus 110 having a CT scanner 118, and imaging apparatus 110′ havinga fluoroscopy system 115. Fluoroscopy system 115 is also herein referredto as an interventional system or a first image acquisition system, andCT scanner 118 is also herein referred to as a 3D model system or asecond image acquisition system.

FIG. 2 depicts an interventional system 115 where a patient 250 on table117 has a catheter 260 placed within an anatomical region 255, such asthe coronary sinus in the patient's heart for example. In an embodiment,catheter 260 is positioned at a known anatomical structure in theanatomical region (such as the coronary sinus at the heart) at alocation defined by the intersection of a horizontal plane 265 and theline 270 joining the focal point 275 of the x-ray source 280 of thefluoroscopy system 115 to the projection of the catheter 260. Otheranatomical regions may include a heart chamber, such as the rightventricle for pacing/defibrillation lead in bi-ventricular pacing, or apulmonary vein for example, and other anatomical structures may includea mitral valve, a pulmonary vein ostia, a junction into an atria, or ajunction into a ventricle, for example. However, embodiments of theinvention are not intended to be limited to only those anatomicalregions and structures disclosed herein. In an exemplary embodiment, thelocation of the horizontal plane 265 is defined by an elevation h abovethe anatomical reference system (table) 117 to the known anatomicalstructure (coronary sinus) at the anatomical region (heart) 255. In thismanner, a known location of the catheter 260 in the fluoroscopy system115 and the 3D model system 118 may be established.

Referring back to FIG. 1, imaging apparatus 110 also includes EKG gatedacquisition or image reconstruction 135 capabilities to image the heartfree of motion, typically in its diastolic phase. Interfacing with EKGmonitor 112 allows real time acquisition of the cardiac electricalimpulses and allows gated acquisition or retrospective reconstruction ofthe acquired data. As mentioned previously during sinus rhythm forexample it could be 75% and during atria fibrillation at about 45% dueto shorter R-R intervals. This allows elimination of the cardiac motionby imaging the heart in the same phase of the diastole. The acquireddata may be stored on a database or used to generate the required imageby using one or more protocols optimized for imaging. In an embodiment,the image data stream from image generation system 140 is communicatedvia link 212 to the operator interface system 160 for display andvisualization, and communication link 216 to processing system 180. Theimage data used by software at operator interface system 160 for examprescription and visualization may be stored in image database 150. Theimaged data may be archived 167, put on a film 168, and/or sent over anetwork 169 to processing system 180 for analysis and review, including3D post-processing. The 3D model image 184 and the fluoroscopy image 182may be viewed singly or in combination on display 186. In the case of AFplanning, post-processing software at processing system 180 allowsdetailed 3D and endocardial views of the left atrium and pulmonaryveins. These images and others may be stored and viewed at the time ofthe interventional procedure.

Imaging apparatus 110 further includes circuitry for acquiring imagedata and for transforming the data into a useable form, which is thenprocessed to create a reconstructed image of features of interest withinthe patient. The image data acquisition and processing circuitry isoften referred to as a “scanner”, regardless of the type of imagingsystem, because some sort of physical or electronic scanning oftenoccurs in the imaging process. The particular components of the systemand related circuitry differ greatly between imaging systems due to thedifferent physics and data processing requirements of the differentsystem. However, it will be appreciated that the present invention canbe applied regardless of the selection of a particular imaging system.

Data is output from imaging apparatus 110 into subsystem 230, whichincludes software to perform data acquisition in data acquisition system120 and image generation in image generation system 140. Data control iseither provided by operator interface system 160 or within subsystem 230via communication link 212. Data that is output from the imagingapparatus 110, including R-peak events 114, is stored in the acquisitiondatabase 130. Data acquisition in system 120 is performed according toone or more acquisition protocols that are optimized for imaging theheart, and specifically for imaging the right atrium and/or coronarysinus.

In an exemplary embodiment, the 3D image data of the atrium is createdusing a protocol that is optimized for the left atrium, such as coronaryartery imaging protocol or CardEP protocol for example. Exemplaryparameters used in these protocols include 0.5 second Gantry periodswith 0.375 helical pitch factors, 120 kilovolts, 250 milliamps and 0.625or 1.25 mm (millimeter) slice thickness. These functions may beperformed with commercially available off the shelf software tools, suchas Advanced Vessel Analysis (AVP) or CardEP for example. After the abovementioned tools are applied to the image data, further processing may beapplied, such as thresholding, floater filtering, and scalping, forexample. These processes are used to clean up the images and may beautomated. Automated processes may require queues from the operator asthe operator is stepped through the process by the operating software.Following the image clean up process, the remaining cardiac chambers areeliminated and only the left atrium is visualized. A detailed 3D imageof the left atrium and the pulmonary veins may then be created. The 3Dand endocardial (view from inside) are visualized using volume renderingtechniques using a variety of volume rendering commercially availablesoftware packages, such as VR and Cardiac Image Quality (CARDIQ) forexample. Once the 3D images are created, the 3D model geometry thenneeds to be registered with that of the fluoroscopy system.

Registration is the process of aligning images. Intra-subjectmulti-modality registration is registration of two different modalitiesin the same patient. The number of parameters needed to describe aTransformation (Registration) is referred to herein as number of“Degrees of Freedom”. An assumption is made that the 3D model behaves asa rigid body, as the anatomy of the anatomical structure beingregistered has not changed significantly. In this case, 3 translationsand 3 rotations, which give 6 degrees of freedom, will lead to asuccessful registration. Each device used for registration needs to becalibrated to approximate the size of the anatomical 3D model. Thisrequires 3 extra degrees of freedom equating to “scaling” in eachdirection. If a set of corresponding anatomical landmarks (fiducials) xand y can be identified, then the registration can be affected byselecting a transformation that will align these areas. Each view in thedevice being used is being referred to as the co-ordinate system thatwill define a space in that view. Successful registration will involvethe determination of a Transformation between the fiducials in one space(X) of one view, for example, with that of another space (Y), forexample. Successful registration will involve determination of aTransformation T between fiducials in the “X” space with those in the“Y” space that minimizes the error T(x)−y, where T(x)=Ry+t, R is theRotation, and t is the translation.

A Transformation matrix defines how to map points from one co-ordinatespace into another co-ordinate space. By identifying the contents of theTransformation matrix, several standard operations, including rotation,translation and scaling, can be performed.

There may be significant difficulty in identifying and aligninganatomical landmarks in two co-ordinate spaces for successfulregistration. Instead of aligning anatomical structures, a uniquefeature of the present invention involves registration performed byaligning the anatomical structures with a tool placed by the physicianin the anatomical structure. Although other tools such as a lead can beplaced in a anatomical structure, such as the right ventricle in thecase of bi-ventricular pacing for example, the embodiment disclosedherein uses a catheter placed in the coronary sinus.

Another embodiment of the invention involves registration of thefluoroscopic image with the 3D model of the anatomical structure. Asdepicted in FIGS. 4A, B and C, which are discussed in more detail below,the coronary sinus catheter positioned in the coronary sinus can beclearly seen on the fluoroscopic projection image. The fluoroscopy imagecan be also used as an interventional system to locate the mapping andablation catheter and or/pacing lead as it is navigated to theappropriate site. A further embodiment of the invention involves usingthe motion of the coronary sinus catheter to determine the phase of theheart motion. Apart from assessing the continuous movement of thechamber, such as the left atrium, the motion of the catheter can also beused to perform registration of the same phase of diastole (75% ofcardiac cycle for example) where the CT image is being reconstructed.

FIGS. 5A, B, C, D, E and F, have been used for validation of theregistration process performed in accordance with an embodiment of theinvention by the injection of contrast in one of the pulmonary veins. Asillustrated, FIGS. 5A, B, C, D, E and F, depict injection of a contrastin the Right superior pulmonary vein (RSPV) through a sheath placed inthe RSPV. The contrast is injected after the registration is completedto assess accuracy of registration. In FIG. 5A, there is no contrast,while FIG. 5B shows injection of the contrast followed by a gradualwashout as shown in subsequent FIGS. 5C, D and E. In FIG. 5F, no morecontrast is seen, suggesting that it has washed out completely. Whilenot specifically delineated, it has been demonstrated that the contrastfilled RSPV nicely superimposes on the RSPV shown on the registered CTimage, suggesting an accurate registration.

The image formation model of the fluoroscopy system is a conicprojection. The location of the center of the projection and theposition of the imaging plane are in principle well described withrespect to an anatomical reference system, such as the patient table 117for example. This anatomical reference system 117 is coherent with thatused to position the 3D model obtained from the CT system 118.

Assuming that an established protocol is followed by an operatingtechnician during the positioning of the patient in the two acquisitionsystems, that is, the fluoroscopy system 115 and the CT system 118, theanatomical reference system 117 may then be considered common to bothacquisitions systems, especially in terms of orientation, that is,rotation between the two reference systems may be considered negligible.

A coronary sinus catheter from the superior vena cava (SVC) is routinelyplaced during the AF interventional procedure. As previously mentioned,and to provide for the registration of the 3D model image 184 with thefluoroscopy image 182, a catheter 260 (depicted in-situ in FIG. 4) isemployed during the operation of fluoroscopy system 115, which will nowbe described with reference to FIG. 3 in combination with FIGS. 1 and 2.As an important aside, however, it should be noted that the geometricalstructure of the catheter 260 may not be sufficiently rich enough toallow a complete registration of the two modalities without employingembodiments of the invention disclosed herein. For example, and in thecase of coronary imaging, a scaling factor computed only from theestablished relationship between the superior or inferior vena cava(SVC, IVC) and the coronary sinus (CS) in conjunction with the catheter260 inside the CS, may not be precise enough for accurate registration.

In FIG. 4A, the 3D model of the left atrium obtained using CT imagingand segmentation in anteroposterior (AP) view is depicted. In FIG. 4B, aprojection image of the heart obtained using fluoroscopy system isdepicted, where multiple catheters including the coronary sinus catheterare positioned at different locations by the physician. As can beappreciated, there is little or no contrast differentiation between thedifferent structures in the fluoroscopic image. In FIG. 4C, a registeredimage using the 3D model of the left atrium and the projection imageusing the fluoroscopy is depicted. Referring to FIGS. 4A, B and Ccollectively, which are all depicted in anteroposterior view, catheter260 is located in the coronary sinus (CS Catheter), the left atrialappendage is designated LAA, the right superior pulmonary vein isdesignated RSPV, the left superior pulmonary vein is designated LSPV,and the mitral valve annulus is designated MV.

FIG. 3 depicts a flowchart of an exemplary method 300 for registering 3Dmodel image 184 with fluoroscopy image 182, where fluoroscopy system 115is used to generate 2D fluoroscopy images (such as x-ray projectionimages) 182, and CT system 118 is used to generate 3D model images 184.Prior to image acquisition, catheter 260 is placed at an anatomicalstructure (such as the coronary sinus) of an anatomical region (such asthe heart) 255 of patient 250 using known techniques. During theacquisition of images 182, 184, a common anatomical reference system(such as the patient table) 117 is used, thereby establishing areferential link between the two imaging systems 115, 118. After imageacquisition, processing circuit 170 processes 305 the image data 182,184 in such a manner, to be discussed in more detail later, as to resultin 3D model 184 being registered 310 with fluoroscopy image 182. Ingeneral, processing circuit 170 utilizes the common reference system 117to link known geometric information between and pertaining to each imageacquisition system 115, 118, and uses discernible parameters associatedwith catheter 260 that are available from both the first and secondimage acquisition systems 115, 118, in order to register the two images182, 184.

During the processing phase 305, pre-processing 315, 320 on images 182,184, respectively, takes place prior to the actual registration process310. During pre-processing 315, the x-ray projection images 182 areanalyzed 325, 330 to determine the likelihood of the apparent catheterimage actually being the catheter 260, and to determine a magnificationfactor X for the x-ray image 182 based on the known actual cathetersize, measured prior to insertion into the patient 250, and the apparentcatheter size, measured or known from the x-ray image 182.

Pre-processing 320 follows both paths 335, 340, where path 335 relatesto the processing of the anatomical structures in the CT model used forregistration, and path 340 relates to the processing of the clinicalstructure that is desired to be displayed following registration. Inaccordance with embodiments of the invention, at least one catheter isdisposed in the superior vena cava SCV and/or coronary sinus CS. Ineither path 335, 340, pre-processing 320 performs a parallel projectionoperation 355 on the 3D model 184 with respect the geometry discerniblefrom the fluoroscopy image 182, thereby properly orienting the 3D model184 with respect to the fluoroscopy image 182. At block 360, image 184is processed to establish the pathway of the catheter 260 in the vesselor vessels of interest, such as the SVC or coronary sinus. At block 365,the result of the processing done at 325 and 330 is used to register theimages 182 with the pathway 360. As a result of this registration, atransformation is identified that links the images 184 and images 182.

At block 310, the registration process involves generating both atranslation factor (x, y) for translating the 3D model 184 with respectto the fluoroscopy image 182, and a scaling factor λ for adjusting thescale of the 3D model 184 with respect to the fluoroscopy image 182. Thetranslation factor is straightforward, and uses known techniques andprocesses, such as aligning the centers of common anatomical structuresfor example. In principle, the alignment method can also compensate fora rotation along an axis perpendicular to the projection plane. However,the scaling factor is not so straightforward and will now be describedby way of alternative examples. In general, however, the scaling factoris dependent on known information from the common anatomical referencesystem 117 and discernable features of the catheter 260.

In a first embodiment, the apparent diameter of the catheter 260 in thefluoroscopy image 182 is determined and then compared with the knownactual diameter of the catheter 260. From this information, the actualdimension of an anatomical structure in the anatomical region 255 in thefluoroscopy image 182 may be determined. The anatomical structure in thefluoroscopy image 182 is then matched with the same anatomical structurein the 3D model 184, where now the actual and apparent sizes of the sameanatomical structure in the 3D model 184 may be compared. From thiscomparison, a scaling factor may be established between the first andsecond image acquisition systems 115, 118.

In a second embodiment, the catheter 260 is disposed at a knownanatomical structure in the anatomical region 255 at a location definedby the intersection of a horizontal plane 265 and the line 270 joiningthe focal point 275 of the fluoroscopy system 115 to the projection ofthe catheter 260 in the fluoroscopy image 182. Here, the horizontalplane 265 is defined by an elevation h above the anatomical referencesystem 117 to the known anatomical structure in the fluoroscopy system115, which establishes a known location of the catheter 260 in thefluoroscopy system 115 and the CT system 118 relative to the anatomicalreference system 117. Knowing the location of the catheter 260 in the 3Dmodel 184 and the actual and apparent dimensions for elevation h in the3D model 184, the actual size of the same anatomical structure in the 3Dmodel 184 as that in the fluoroscopy image 182 may be determined. Bycomparing the actual and apparent sizes of the anatomical structure inthe 3D model 184, a scaling factor between the first and second imageacquisition systems 115, 118 may be established.

In a third embodiment, the fluoroscopy system 115 is used to produce afirst and a second set of fluoroscopy projection images, which aregenerated using at least two different x-ray projections separated by anangle sufficient to produce discernibly different projection images ofthe anatomical region 255. Here, as in other embodiments, the catheter260 is disposed at a known anatomical structure in the anatomical region255. By analyzing the two sets of projection images using a knowntriangulation approach, the location of the catheter 260 in the 3D model184 with respect to the focal point 275 of the x-ray source 280 of thefluoroscopy system 115 may be determined, thereby defining a dimensionb, which establishes a known location of the catheter 260 in thefluoroscopy system 115 and the CT system 118 relative to the focal point275. Knowing the location of the catheter 260 in the 3D model 184 andthe actual and apparent dimensions for dimension b in the 3D model 184,the actual size of the same anatomical structure in the 3D model 184 asthat in the fluoroscopy image 182 may be determined. By comparing theactual and apparent sizes of the anatomical structure in the 3D model184, a scaling factor between the first and second image acquisitionsystems 115, 118 may be established.

While exemplary embodiments disclosed herein reference the size of thecatheter 260 for scaling purposes, it will be appreciated that othermeasurable features may also be used for scaling, such as theinterelectrode distance at the catheter 260, for example. Accordingly,embodiments of the invention are not intended to be limited to only areference to the size of catheter 260 for scaling purposes.

To avoid possible jitter of the registered image of the 3D model 184 dueto cyclical movement of the heart, or other anatomical region 255 ofinterest, the processing circuit 170 may be responsive to additionalexecutable instructions for registering the 3D model 184 with thefluoroscopy image 182 in synchronization with the cyclical movement ofthe anatomical region 255, that is, in synchronization with the cyclicalmovement of a heart beat.

With the registration of 3D model 184 with fluoroscopy image 182 havingbeen established, reference will now be made to FIG. 6, which depicts ageneralized flowchart of a registration method 400 for registering the3D model 184 of anatomical region 255 of patient 250 with acatheter-based tracking system 405, best seen by referring to FIG. 7. InFIG. 6, the registration of 3D model 184 with fluoroscopy image 182 isreferred to as a first registration R1, and the registration ofcatheter-based tracking system 405 with fluoroscopy image 182 isreferred to as a second registration R2. Catheter-based tracking system405 is generally referred to as an interventional tracking system sinceit may or may not include a catheter. For example, tracking system 405may include a pacing and/or defibrillation lead. In an embodiment,catheter-based tracking system (tracking system) 405 includes catheter260 having a position indicator 410 and an ablating electrode 415.Position indicator 410 may be a miniature coil, three miniatureorthogonal coils, or any other position indicating device suitable forproviding signals representative of its coordinates with respect to adefined second anatomical reference system 420 (with anatomicalreference system (table) 117 being referred to as a first anatomicalreference system). In an embodiment, second anatomical reference system420 is a coordinate system common to both the tracking system 405 andthe fluoroscopy image 182 of the fluoroscopy system 115. Signals fromposition indicator 410 are communicated to processing circuit 170 viacatheter lead 262, communication link 218 or communication links 210 and212. By using the (second) common anatomical reference system 420 andthe signals from position indicator 410, processing circuit 170, beingconfigured to execute appropriately coded instructions, is capable ofregistering the catheter-based tracking system 405 with the fluoroscopyimage 182 and fluoroscopy system 115.

In addition to the previously discussed techniques for registering the3D model 184 with the fluoroscopy image 182, processing circuit 170 isalso configured to process executable instructions for recording thelocation of a first position of catheter 260 in fluoroscopy image 182,and in response to signals from position indicator 410, recording therespective coordinates of catheter 260 at the first position. By thenregistering the location information with the coordinate information,position indicator 410 may be registered with the fluoroscopy image 182.In general, proper registration of the catheter-based tracking system405 with the fluoroscopy system 115 requires at least three data pointsassociated with position indicator 410, with each image location andrespective coordinate location being recorded. However, for enhancedaccuracy, an embodiment of processing circuit 170 is configured toregister a multitude of data points associated with position indicator410.

Due to system variables, the position signals from position indicator410 may not be capable of providing exact coordinates for the locationof position indicator 410, providing instead only an approximation forthe coordinates. While the approximation may be quite good, itnonetheless may still be only an approximation. In such an instance, anembodiment of processing circuit 170 may be configured to compute aprobability function representative of the probability of catheter 260,or more specifically position indicator 410, being at the coordinatesindicated by the signals from position indicator 410. An exemplaryprobability function is illustrated in FIG. 8 as a sphere 425, whichdefines a probability region that is representative of a region in thefluoroscopy image 182, and the registered 3D model 184, where the tip ofcatheter 260 is probably, more likely than not, located. While FIG. 8depicts the x, y and z, positional distribution functions 430, 435 and440, to be normal bell-shaped distribution functions, it will beappreciated that this is exemplary only, and that any distributionfunction may be substituted therefore. Here, processing circuit 170 maybe programmed for computing a probability function representative of theprobability of the pacing and/or defibrillation lead being at thecoordinates indicated by the signals from the position indicator, andapplying the probability function to the 3D model to define aprobability region representative of a region in the 3D model where thelead is probably located.

While embodiments of the invention disclose a heart as an exemplaryanatomical region, it will be appreciated that the invention is not solimited and that the scope of the invention includes other anatomicalregions of interest within the patient. While embodiments of theinvention disclose a coronary sinus as an exemplary anatomical structurewithin an anatomical region, it will be appreciated that the inventionis not so limited and that the scope of the invention includes otheranatomical structures within an anatomical region. While embodiments ofthe invention disclose a catheter placed within the patient, it will beappreciated that the invention is not so limited and that the scope ofthe invention includes other devices discernable via x-ray and CT, suchas a pacing and/or defibrillation lead for example.

An embodiment of the invention may be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present invention may also be embodied in the form of acomputer program product having computer program code containinginstructions embodied in tangible media, such as floppy diskettes,CD-ROMs, hard drives, USB (universal serial bus) drives, or any othercomputer readable storage medium, wherein, when the computer programcode is loaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. The present invention may alsobe embodied in the form of computer program code, for example, whetherstored in a storage medium, loaded into and/or executed by a computer,or transmitted over some transmission medium, such as over electricalwiring or cabling, through fiber optics, or via electromagneticradiation, wherein when the computer program code is loaded into andexecuted by a computer, the computer becomes an apparatus for practicingthe invention. When implemented on a general-purpose microprocessor, thecomputer program code segments configure the microprocessor to createspecific logic circuits. The technical effect of the executableinstructions is to register a 3D model with a fluoroscopy image for atleast the purpose of assisting in a medical intervention procedure.

As disclosed, some embodiments of the invention may include some of thefollowing advantages: the availability of a CT-Fluoro registrationtechnique that will allow pacing leads to be navigated and placed at themost appropriate site, thereby improving the effectiveness ofbi-ventricular or left ventricle pacing; the availability of a CT-Fluororegistration technique that will show the location of the coronary sinuson the 3D model, thereby eliminating the need in bi-ventricular pacingto perform coronary sinus angiography prior to implantation of thecoronary sinus lead; the ability to use the coronary sinus catheter inAF ablation for continuous registration; for a given orientation of theinterventional system, the ability to automatically generate aprojection of the 3D model that is geometrically close to the imageprovided by the interventional system; the ability to merge theinformation obtained from a 3D model generated using a scanner with thereal-time live information provided by fluoroscopy imaging; theavailability of a technique that will allow visualization of the true 3Dgeometry of the different pulmonary vein—left atrial junction and otherstrategic areas in the atria by using imaging capabilities of the CT,and more importantly registering these images with X-ray fluoroscopy, tohelp isolate the pulmonary veins and these areas which initiate andsustain AF more precisely and easily; and, the ability to accurately andcontinuously track the real-time movement of a catheter during aninterventional procedure.

Furthermore, embodiments of the invention may be used to navigate adelivery system, such as a catheter or a sheath apparatus (depictedgenerally as catheter 260), for delivery of other forms of therapies,such as stent delivery, in coronary artery disease, delivery of cells,genes or other forms of therapies to the appropriate sites as needed.Here, processing circuit 170 may be programmed for generating afluoroscopy image of the anatomical region from the fluoroscopy system,the anatomical region having disposed therein a catheter, generating a3D model of the anatomical region from the second image acquisitionsystem of a different modality, analyzing the fluoroscopy image and the3D model with respect to a common anatomical reference system,monitoring the introduction of a catheter delivery apparatus into theanatomical region of interest, navigating the catheter deliveryapparatus over the registered model to an anatomical site of interest,and using the catheter delivery apparatus to deliver therapy. While theinvention has been described with reference to exemplary embodiments, itwill be understood by those skilled in the art that various changes maybe made and equivalents may be substituted for elements thereof withoutdeparting from the scope of the invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the invention without departing from the essentialscope thereof. Therefore, it is intended that the invention not belimited to the particular embodiment disclosed as the best or only modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

1. An imaging system for use in a medical intervention procedure,comprising: a first image acquisition system configured to produce afluoroscopy image of an anatomical region; a second image acquisitionsystem configured to produce a 3D model of the anatomical region; aninterventional tracking system configured to maneuver within theanatomical region, the interventional tracking system comprising aposition indicator, a first anatomical reference system common to boththe first and the second image acquisition systems; a second anatomicalreference system common to both the first image acquisition system andthe interventional tracking system; and a processing circuit configuredto process executable instructions for: registering the second imageacquisition system with the first image acquisition system to define afirst registration; registering the interventional tracking system withthe first image acquisition system to define a second registration; andin response to the first and second registrations, registering theinterventional tracking system with the second image acquisition system.2. The imaging system of claim 1, wherein: the interventional trackingsystem further comprises a catheter; the registering the second imageacquisition system with the first image acquisition system comprisesregistering the 3D model with the fluoroscopy image; and the registeringthe interventional tacking system with the first image acquisitionsystem comprises registering the position indicator with the fluoroscopy3. The image system of claim 2, wherein: the registering the 3D modelwith the fluoroscopy image comprises registering the 3D model with thefluoroscopy image in response to the first common reference system anddiscernible parameters associated with the catheter in both the firstand second image acquisition systems; and the registering the positionindicator with the fluoroscopy image comprises registering the positionindicator with the fluoroscopy image in response to the second commonreference system and signals representative of the position of theposition indicator.
 4. The imaging system of claim 3, wherein: in thefirst image acquisition system, the catheter is disposed at ananatomical structure within the anatomical region; and the processingcircuit is further configured to process executable instructions for:generating a translation factor for translating the 3D model withrespect to the fluoroscopy image; and generating a scaling factor foradjusting the scale of the 3D model with respect to the fluoroscopyimage, the scaling factor being dependent on a discernable feature ofthe catheter.
 5. The imaging system of claim 4, wherein the catheter hasa known actual diameter, and wherein the processing circuit is furtherconfigured to process executable instructions for: determining theapparent diameter of the catheter in the fluoroscopy image, comparingthe apparent diameter of the catheter with the known actual diameter ofthe catheter, determining in response thereto an actual dimension of ananatomical structure in the anatomical region in the fluoroscopy image,matching the anatomical structure in the fluoroscopy image with the sameanatomical structure in the 3D model, comparing the actual and apparentsizes of the same anatomical structure in the 3D model, and generatingtherefrom a scaling factor between the first and second imageacquisition systems.
 6. The imaging system of claim 4, wherein: thecatheter is disposed at a known anatomical structure in the anatomicalregion at a location defined by the intersection of a horizontal planeand the line joining the focal point of the fluoroscopy system to theprojection of the catheter, the horizontal plane being defined by anelevation h above the anatomical reference system to the knownanatomical structure in the fluoroscopy system, thereby establishing aknown location of the catheter in the first and second image acquisitionsystems; and the processing circuit is further configured to processexecutable instructions for: determining the actual size of the sameanatomical structure in the 3D model in response to the known locationof the catheter in the 3D model and the elevation h, comparing theactual and apparent sizes of the anatomical structure in the 3D model,and generating therefrom a scaling factor between the fit and secondimage acquisition systems.
 7. The imaging system of claim 4, wherein;the first image acquisition system is further configured to produce asecond set of fluoroscopy projection images, the f and second sets ofprojection images being generated by at least two different x-rayprojections separated by an angle sufficient to produce discerniblydifferent projection images of the anatomical region, the catheter bedisposed at a known anatomical structure in tee anatomical region; andthe processing circuit is further configured to process executableinstructions for: determining the location of the catheter in the 3Dmodel with respect to the focal point of the fluoroscopy system todefine a dimension b by analyzing the two sets of projection imagesusing a triangulation approach; and determining the actual size of thesame anatomical structure in the 3D model in response to the knownlocation of the catheter in the 3D model and the dimension b, comparingthe actual and apparent sizes of the anatomical structure in the 3Dmodel, and generating therefrom a scaling factor between the first andsecond image acquisition systems.
 8. The imaging system of claim 4,wherein the processing circuit is further configured to processexecutable instructions for: recording the location of a first positionof the catheter in the fluoroscopy image; in response to the signalsfrom the position indicator, recording the coordinates of the catheterat the first position; and register the location information with thecoordinate information thereby register the position indicator with thefluoroscopy image.
 9. The imaging system of claim 8, wherein theprocessing circuit is further configured to process executableinductions for; recording at least three locations of at least a first,a second and a third, position of the catheter in the fluoroscopy image;in response to the signals from the position indicator, recording thecoordinates of the catheter at the at least a first, a second and athird, position; and registering the location information with thecoordinate information thereby registering the position indicator withthe fluoroscopy image.
 10. The imaging system of claim 9, wherein theprocessing circuit is further configured to process executableinstructions for: computing a probability function representative of theprobability of the catheter being at the coordinates indicated by thesignals from the position indicator; and applying the probabilityfunction to the 3D model to define a probability region representativeof a region in the 3D model where the catheter is probably located. 11.The imaging system of claim 9, wherein the processing circuit is furtherconfigured to process executable instructions for: computing aprobability function representative of the probability of the pacingand/or defibrillation lead being at the coordinates indicated by thesignals from the position indicator, and applying the probabilityfunction to the 3D model to define a probability region representativeof a region in the 3D model where the lead is probably located.
 12. Theimaging system of claim 1, wherein: the anatomical region comprises aheart, a heart chamber, a pulmonary vein, or any combination comprisingat least one of the foregoing.
 13. The imaging system of claim 4,wherein: the anatomical structure comprises a coronary sinus, a mitralvalve, a pulmonary vein ostia, a junction into an atria, a junction intoa ventricle, or any combination combing at least one of the forgoing.14. The imaging system of claim 1, wherein: the first image acquisitionsystem comprises a 2D fluoroscopy system; and the second imageacquisition system comprises at least one of a CT system, a MR system,an Ultrasound system, a 3D fluoroscopy system, and a PET system.
 15. Theimaging of claim 8, wherein the processing circuit is further configuredto process executable instructions for registering the 3D model with thefluoroscopy image in synchronization with cyclical movement of a heart.16. A method of registering a 3D model of an anatomical region of apatent with a catheter-based tracking system, the catheter-based tackingsystem comprising a catheter with a position indicator, the methodcomprising: generating a fluoroscopy image of the anatomical region, thecatheter with the position indicator being disposed within theanatomical region; generating a 3D model of the anatomical region; usinga first common anatomical reference system and a discernible parameterassociated with the catheter, registering the 3D model with thefluoroscopy image, thereby defining a first registration; using a secondcommon anatomical reference system and signals from the positionindicator representative of the location of the catheter in thefluoroscopy image, registering the catheter-based system with thefluoroscopy image, thereby defining a second registration; using thefirst registration and the second registration, registering the 3D modelwith the catheter-based tracking system.
 17. The method of claim 16,wherein the registering the 3D model with the fluoroscopy imagecomprises: generating a translation factor for translating the 3D modelwith respect to the fluoroscopy image; and generating a scaling factorfor adjusting the scale of the 3D model with respect to the fluoroscopyimage, the scaling factor being dependent on a discernable feature ofthe catheter.
 18. The method of claim 17, wherein the registeringcomprises: registering the 3D model with the fluoroscopy image insynchronization with cyclical movement of a heart.
 19. The method ofclaim 16, wherein the 3D model is generated using a CT system, a MRsystem, an Ultrasound system a 3D fluoroscopy system, a PET system, orany combination comprising at lent one of the foregoing.
 20. A cuterprogram product for registering a 3D model of an anatomical region of apatient with a catheter-based tracking system, the catheter-basedtracking system comprising a catheter with a position indicator, theproduct comprising: a storage medium, readable by a processing circuit,storing instructions for execution by the processing circuit for:generating a fluoroscopy image of the anatomical region, the catheterwith the position indicator being disposed within the anatomical region;generating a 3D model of the anatomical region; using a first commonanatomical reference system and a discernible parameter associated withthe catheter, registering the 3D model with the fluoroscopy image,thereby defining a first registration; using a second common anatomicalreference system and signals from the position indicator representativeof the location of the catheter in ate fluoroscopy image, registeringthe catheter-based tracking system with the fluoroscopy image, therebydefining a second registration; and using the first registration and thesecond registration, registering the 3D model with the catheter-basedtracking system; wherein the first registration comprises generating atranslation factor for translating the 3D model with respect to thefluoroscopy image, and generating a scaling factor for adjusting thescale of the 3D model with respect to the fluoroscopy image, the scalingfactor being dependent on a discernable feature of the catheter.
 21. Acomputer program product for registering a 3D model of an anatomicalregion of a patient with projection image of the same from aninterventional fluoroscopy system, the product comprising: a storagemedium, readable by a processing circuit, storing instructions forexecution by the processing circuit for: generating a fluoroscopy imageof the anatomical region from the fluoroscopy system, the anatomicalregion having disposed therein a catheter; generating a 3D model of toanatomical region from a second image acquisition system of a differentmodality, analyzing the fluoroscopy image and the 3D model with respectto a common anatomical reference system; monitoring the introduction ofa catheter delivery apparatus into the anatomical region of interest;navigating the catheter delivery apparatus over the registered model toan anatomical site of interest; and using the catheter deliveryapparatus to deliver therapy,
 22. The imaging system of claim 1,wherein: the interventional tracking system further comprises adefibrillation and/or pacing lead; the registering the second imageacquisition system with the first image acquisition system comprisesregister the 3D model with the fluoroscopy image; and the registeringthe interventional tracking system with the first image acquisitionsystem comprises registering the position indicator with the fluoroscopyimage
 23. The imaging and tracking system of claim 1, wherein; theregistering the interventional tracking system with the first imageacquisition system is performed using a defibrillation and/or pacingload.